Control arrangement for food heating device

ABSTRACT

A control arrangement for an electric food heating device having heating elements for heating foodstuff and providing a source of light impinging on the foodstuff, the control arrangement comprising: a peaking circuit (42, 30) to determine maximum reflected light from the foodstuff and provide a first signal (VI), and measuring subsequently reflected light from the foodstuff and providing a second signal (V2), said peacking circuit including amplifier means (30) for determining the difference between the first and the second signals, and providing a third signal (V3); and a comparator means (26) for comparing the third signal (V3) and a preset signal (VB), the preset signal being proportionate to a desired heating level, the comparator means providing a terminating signal (DONE) to deactivate heating when the preset and the third signals are substantially equal.

FIELD OF THE INVENTION

The present invention relates to electric toasters and associatedcontrol means. In particular, the present invention relates to providingapparatus for controling, regulating and/or sensing the extent oftoasting.

BACKGROUND OF THE INVENTION

Various food products each require a varying degree of toasting in orderto effect a desired "browness". For example, bread, muffins, crumpetsand other food products each exhibit a varying degree of inherentuntoasted browness, which inherent browness often results in excessiveor inadequate toasting of the food product.

Conventional toasters perform adequately when set with respect to whitebread but may over-toast brown bread and toasters which performadequately when set with respect to brown bread may under-toast whitebread. Compensation for the above may be effected by adjusting thetoaster. This is often not precise and is often otherwise inconvenientor easily forgotton.

Furthermore, few toasters additionally incorporate a "warmup" feature,independent of a toasting function. Also, should the toaster beactivated, without any food product therein, often hazardous toasteroperation occurs, as a result of excessive heat.

U.S. Pat. No. 2,436,575 discloses a toaster which uses light emanatingfrom a light source and reflected from toast, and measured eithercontinuously or discontinuously, to produce a controlling current, whichcurrent operates a series of relays. When the current achieves apredetermined magnitude, the activated relays terminate the toastingoperation. The specification also discloses a momentary delay operationto allow the photoelectric cell time to attain equilibrium when firstmeasuring untoasted bread. U.S. Pat. No. 2,436,575 does not disclose atoaster wherein compensation for browness is effected dependent on thefood product to be toasted.

U.S. Pat. No. 3,956,978 discloses a switching mechanism for a toaster toterminate supply of electricity to the toasting elements. Thisspecification also discloses an alternative circuit which measures toastbrowness via light reflected from a separate light source in the toasterand also discloses a differential amplifier which triggers thetermination of toasting when a desired browness is reached. However, thedisclosed arrangement does not establish a signal which is needed tocompensate for different bread types.

U.S. Pat. No. 4,363,957 discloses apparatus adapted to cook or charvaried foodstuffs wherein the degree of charring is varied for eachfoodstuff. The control circuit described appears to generally disclose acircuit which stores a voltage representative of the maximum voltageprovided by the optical sensor, that is minimum resistance of the sensoror maximum reflectively of the article, and uses this as a comparisondatum in a comparator to compare changes or decreases in voltage as thearticle chars, to turn the power off at a certain changed level. U.S.Pat. No. 4,363,957 does not disclose the general concept of using a peakholding circuit to establish a reference representative of the maximumreflected light from the untoasted bread, measuring subsequent reflectedlight for the bread as it is being browned, comparing these results witha preset voltage representative of desired browning and terminating thetoasting cycle when reaching the preset voltage in a toaster. Thedisclosure relies on a light source other than the toaster elements. Thedisclosure further does not teach a toaster having a timed warmupsystem, independent of the light sensor technique and also does notdisclose a failsafe mechanism.

U.S. Pat. No. 4,426,572 relates to an improvement to U.S. Pat. No.4,363,957. This disclosure deals with apparatus which more accuratelymeasures light reflected from foodstuff being toasted. U.S. Pat. No.4,433,232 relates to a further improvement to U.S. Pat. No. 4,363,957and U.S. Pat. No. 4,426,572. This disclosure deals with the problem ofaccurately measuring the browness of foodstuff being browned, byavoiding the problem of light reflecting from the surface of thefoodstuff.

U.S. Pat. No. 4,245,148 relates to a food browning device. The foodbrowness is measured and dependent on surface colour. However, thespecification does not disclose an apparatus which compensates itsbrowness measurement according to the different types of foods beingbrowned.

AU 66679/81 discloses a toaster which includes two light detectors, onearranged to monitor light emitted from a light source, the otherarranged to monitor light reflected from an item being cooked.AU66679/81 does not disclose a toaster incorporating a warm-up feasture,nor a toaster which includes a failsafe feature. AU66679/81 does notdisclose that the desired browness of various toasted foodstuffs issubstantially equal when comparing the change in light reflected to amaximum amount of reflected light. The present invention is arranged toeffect this.

DE 2,125,423 discloses a toaster which utilizes reflected light tomeasure the degree of brownness of toast irrespective of the type ofbread being toasted or the moisture content thereof. With reference toFIG. 1, toast 3 is heated by electric element 1. Lights 5 and 51 reflectlight from the toast to photocells 6 and 7. A mirror 15 is used toconcentrate more radiant heat in area 19 on the toast than area 18. Thedesired degree of browness is measured by electronics 16 by comparingthe brownness of areas 18 and 19. DE 2,125,423 does not discloseobtaining a maximum signal after which browness is measured, nor awarm-up feature.

DE 2,152,927 discloses a toaster which also utilizes reflected light tomeasure the degree of brownness of toast. However, it does not providecompensation for browning different types of bread, and accordingly, nomaximum signal is derived after which brownness is measured.Furthermore, no warm-up feature or failsafe feature is disclosed.

JP,A, 57-198928 discloses a roaster wherein, with reference to FIG. 1,when toasting commences, capacitor 19 charges to level corresponding toa standard or the toast's initial reflectivity. After this switch 17 isswitched over to begin browning of the bread, until the toast brownessequals the value set on variable resistor 21. This specification doesnot provide a third signal, nor is there a disclosure as to what effectschangeover of switch 17 to terminal "c", so that the toaster obtains abrowness difference signal from the maximum value on capacitor 19. Thepresent invention does not use a separate light source to irradiate thebread in the roaster, but uses the toasting elements to both radiatedheat and enlighten the bread. The present invention also constantlysenses the bread for a maximum light reflectivity, and so a moreaccurate assessment is made and a more consistent degree of browning isachieved between different types of toasted bread.

The present invention also uses one amplifier to initiate a maximum orpeaking signal and provides or measures a difference signal. Use of oneamplifier alleviates compensation and errors occurring as a result ofmore than one amplifier being used to measure and determine toastbrownness.

OBJECTS OF INVENTION

An object of the present invention is to alleviate the disadvantages ofthe prior art.

A further object of the present invention is to provide a toasteradapted to compensate toasting browness generally in accordance with tothe particular foodstuff being toasted.

A still further object of the present invention is to provide a timedwarmup function independant of the compensated toaster and/or a timedfailsafe mechanism to deactivate the toaster after a prescribed time.

SUMMARY OF THE INVENTION

The present invention may provide a control arrangement or an electricfood heating device having heating elements for heating foodstuff andsaid heating elements providing a source of light impinging on thefoodstuff, the control arrangement comprising:

a peaking circuit to determine maximum reflected light from thefoodstuff and provide a first signal, and measuring subsequentlyreflected light from the foodstuff and providing a second signal, saidpeaking circuit including an amplifier directly responsive to themaximum reflected light for initiating the development of the firstsignal and further for determining the difference between the first andthe second signals, and providing a third signal; and

a comparator means for comparing the third signal and a preset signal,the preset signal being proportionate to a desired heating level, thecomparator means providing a terminating signal to deactivate heatingwhen the preset and the third signals are substantially equal.

The heating level of the control arrangement described above maycorrespond to a desired browning level.

The control arrangement described above may further include:

a timed circuit for warming or lightly toasting the foodstuff,independent of the peaking circuit, comprising a first timed signaloperative to deenergize the heating elements after a preset time.

The control arrangement described above may further include:

a failsafe circuit adapted to deactivate the toasting elements after aprescribed time, the failsafe circuit providing a timed signal operativeto deenergize the heating elements after the prescribed time.

The control arrangement described above may further include:

a failsafe circuit adapted to deactivate the toasting elements after aprescribed time, the failsafe circuit providing a second timed signaloperative to deenergize the heating elements after the prescribed time.

The control arrangement described above may further comprise an initialdelay circuit for avoiding power-on glitches.

The present invention may provide a control arrangement described abovewherein during warming or lightly toasting foodstuff, said preset signalis provided by a fixed voltage divider.

The invention may provide a control arrangement described above whereinsaid preset signal is provided by a source of first voltage, said presetsignal being a fraction of said first voltage and being determined inconjunction with a first voltage divider.

The invention may provide a control arrangement described above whereinsaid preset signal is further provided by a source of second voltage,the second voltage being of larger magnitude than the first voltage andbeing coupled via the first voltage divider, the preset signal being ofa magnitude substantially between said first and said second voltages.

The invention may provide a control arrangement described above whereinthe preset signal is subtracted from the third signal.

The control arrangement described above may further comprise a firstvoltage source coupled to a second voltage divider, the dividerproviding a divided signal to be compared with said preset signal andproviding a warm signal when said divided and said preset signals aresubstantially equal, the warm signal serving to deactivate heating whenthe foodstuff is slightly browned.

The invention may provide a control arrangement described above whereinthe preset signal is provided by a first voltage divider coupled to saidfirst voltage source.

The invention may provide a control arrangement described above whereinthe first voltage divider is also coupled to a source of second voltage,the second voltage being larger in magnitude than said first voltage.

The control arrangement described above may further comprise a source offirst voltage coupled to said peaking circuit, and wherein said firstsignal is provided in response to the differential between said firstvoltage and a heating level voltage representative of the heating ofsaid foodstuff.

The invention may provide a control arrangement described above whereinthe first signal is stored in a voltage storage means, and wherein aunidirectional current element is coupled to the storage means tosubstantially prevent discharge of said first signal.

The invention may provide a control arrangement described above whereinthe peaking circuit includes a first amplifier coupled to provide aheating signal indicative of the level of foodstuff heating, and

a second amplifier coupled to the first amplifier and forming a feedbackloop therewith, the second amplifier adapted to provide said firstsignal in proportion to the difference between said heating signal and areference signal.

The invention may provide a control arrangement described above whereinthe peaking circuit includes a light receiving element adapted todetermine the magnitude of said first signal.

The invention may provide a control arrangement described above whereina light receiving element is coupled to vary the gain of said firstamplifier in response to the measure of reflected light.

The present invention may also provide a control arrangement for a foodheating device having heating elements for browning foodstuff and saidheating elements providing a source of light impinging on the foodstuff,the control arrangement comprising:

means for determining maximum reflected light from the foodstuff andproviding a first signal in response thereto;

means for measuring subsequently reflected light from the foodstuff andfor providing a second signal in response thereto;

said means for determining maximum reflected light also being adapted todetermine the difference between the first and the second signals andprovide a third signal representative of the difference;

means for establishing a preset signal which is proportionate to adesired level of browning of the foodstuff; and

comparator means for comparing the third signal and the preset signal,the comparator means providing a terminating signal to deactivatebrowning when the preset and the third signals are substantially equal.

The invention may provide an electric food heating device including acontrol arrangement described above.

The present invention may provide a toaster having toasting elements forbrowning foodstuff and providing a source of light impinging on thefoodstuff, the toaster including a control arrangement having anindependent timed circuit for warming or lightly toasting the foodstuffprior to normal toasting, said timed circuit being adapted to provided atimed signal operative to deenergize the toasting elements after apreset time.

The present invention may provide a toaster having toasting elements forbrowning foodstuff and providing a source of light impinging on thefoodstuff, the toaster including a control arrangement having a failsafecircuit adapted to deactivate the toasting elements after a prescribedtime, the failsafe circuit providing a timed signal operative todeenergize the toasting elements after the prescribed time.

The present invention may provide in a toaster a peak detectorcomprising:

a light detector for providing a first output proportionate to lightreceived by said detector,

a first amplifier coupled to said detector, the first amplifier having again proportionate to said first output, the first amplifier alsocoupled to a first reference, and having a second output,

a second amplifier coupled to said first amplifier so as to form aclosed or feedback loop,

the second output being provided to said second amplifier together witha second reference and providing a third output,

the third output being provided to a storage means and to said firstamplifier,

the storage means providing an indication of the measure of a peak leveldetected.

The peak detector described above may further comprise:

a diode means interposed said third output and said storage means, thediode substantially preventing leakage of said third output.

The invention may provide a peak detector described above wherein thethird output is proportional to the difference between the second outputand said second reference.

The invention may provide a peak detector described above wherein saidthird output is feedback to said first amplifier to provide a measure ofchange of said first output.

The present invention may provide a toaster including the aforementionedpeak detector.

The toaster described above may further include a variable voltagedivider coupled to said second reference for providing a desiredfoodstuff heating level signal.

The toaster described above may further include a comparator adapted toprovide a done signal when said second output substantially equals saiddesired level signal, the done signal effecting deactivation offoodstuff heating.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described, byway of example only, with reference to the accompanying drawings,wherein:

FIG. 1 shows a toaster of the present invention in block diagram form;

FIGS. 2 and 3 show one form of circuit diagram of a toaster according tothe present invention;

FIGS. 4a-4c show, graphically, voltages at various points in the circuitdiagram of FIG. 3;

FIG. 5 shows a comparison of light reflectivity (shown as an inverse ofresistivity) for various types of foodstuffs;

FIG. 6 shows a power supply suitable for FIGS. 2 and 3; and

FIG. 7 shows a microprocessor form of the present invention.

The circuit shown in FIGS. 1, 2 and 3 comprises a light sensor circuit(1) provided with feedback means to sample and hold a measure of themaximum value of light reflected from a food product to be toasted, acomparator (2) for comparing light reflected from that food productafter detecting said maximum value and a predetermined degree ofbrowness, which, when that comparison equals the predetermined degree ofbrowness represented by a fraction of said measure determined by asetting potentiometer (3), causes a signal to pass to an eject solenoid(4) to deactivate the toaster element and/or to eject the food productfrom the toaster. A failsafe timeout circuit (5) is also provided toavoid hazardous operation in the event that the toaster is accidentallyactivated, by deactivating the toaster after a predetermined period oftime.

The voltages and values herein described are exemplary only, and can bevaried without affecting the operation of the present invention, aswould be known by those skilled in the art.

As illustrated in FIG. 6, a power circuit 10 includes a regulator 12 anda capacitor 14 which are connected across an AC source (not shown) toprovide a D.C. voltage output of 12 volts. The D.C. voltage is used topower components of the toaster.

Referring to FIG. 2, a reference voltage (V_(ref)) of 6 volts appears atthe output of an amplifier 16 while a voltage of 10 volts appears at theoutput of a second amplifier 18. V_(ref) sets the levels throughout thetoaster circuit. A voltage divider which includes a resistor 20 and apotentiometer 22 is connected between the outputs of the amplifiers 16and 18 with a 25 millivolts drop appearing across resistor 20. Thisprovides a voltage range between 6.025 volts (V_(A)) and 10 volts(V_(c)) for potentiometer 22. A voltage V_(B) appears at the center armof potentiometer 22 which is connected to the negative input of each ofa "warmup" comparator 24 and a "done" comparator 26. The positive inputof "warmup" comparator 24 is connected to one side of a resistor 28 theother side of which is connected to V_(ref). There is a voltage drop of40 millivolts across resistor 28 whereby a potential of 6.04 volts(V_(D)) appears at the positive input of comparator 24.

A light-reflective monitoring circuit having an integral peak detectioncapability includes a first op-amp 30. Op amp 30 includes a feedbackloop with a light dependent resistor (LDR) 32 coupled between the outputand the negative input of the amplifier. A reference source 34 of 1.25volts is coupled through resistors 36 and 38 to the negative input ofop-amp 30. Resistors 36 and 38 are valued at 700 ohms and 300 ohmsrespectively to provide a total of 1K ohms. A center tap 40 is providedin the event less input resistance is desired. Reference source 34provides an offset voltage for the negative input of op-amp 30 to startthe circuit properly without introducing noise from the positive supplyinto the loop.

The light-reflective monitoring circuit also includes a second op-amp 42having V_(ref) coupled to its positive input and the output of op amp 30coupled to its negative input. The output of op-amp 42 is coupledthrough a diode 44 to a capacitor 46 and also to the positive input ofop-amp 30.

A third op-amp 48 couples the output of op-amp 30 to the positive inputof comparator 26 through a diode 50 and is clamped by a capacitor 52.Op-amp 48 is used to eliminate the small amount of 50/60 Hz. ripplepicked up by the LDR 32. This ripple can be as high as 200 millivoltspeak to peak depending on ambient lighting conditions, (FIG. 4c).

The following table lists the designations for various voltages in thecircuit illustrated in FIG. 2:

V_(ref) --output of amplifier 16

V_(A) --low side of potentiometer 22

V_(B) --center arm of potentiometer 22

V_(C) --high side of potentiometer 22

V_(D) --positive input of comparator 24

V₁ --positive input of op amp 30

V₂ --negative input of op amp 30

V₃ --output of op amp 30

V₄ --output of op amp 42

V₅ --output of op amp 48

V₆ --positive input of comparator

When the toaster is to be used, the user manually adjusts the center armof potentiometer 22 to a position representative of the desired level ofbrowning of the bread. The bread is then placed on the toaster elevatorwhich is then lowered whereby the toaster is initially operated.Referring to FIG. 3, reset signal POR is then developed by a resetcircuit 54 and is coupled to and resets a pair of flip-flops 56 and 58as well as a timer 60. Also, a clock 62 develops either 50 Hz or 60 Hzsquare wave CLOCK and CLOCK outputs. The CLOCK output is coupled totimer 60 and flip-flop 58 while the CLOCK output is coupled to a timer64. The RESET output of flip-flop 56, which is initially low, isconnected to the "B" input of an AND gate 66 whereby the output of thegate is held low.

The output of AND gate 66 is coupled to a SCR driver 68 which applies abias to a gate 70 of a SCR 72. SCR 72 controls the actuation of a coil74 of a solenoid which initiates the raising of the bread-supportingelevator of the toaster and also facilitates the shut down of theelectronics of the toaster at the appropriate time.

Based on a 60 Hz. output from clock 62, timer 60 develops output signalsat 4 seconds, 35 second and 135 seconds after the toaster has beeninitially operated. The 4-seconds signal is fed to flip-flop 56 wherebythe RESET output of the flip-flop goes high and prepares AND gate 66 sothat, upon application of a high signal to the "A" input of the ANDgate, the output of the gate will go high. This provides a four seconddelay after toaster start-up to allow for transient start-upinterference to settle down before effective monitoring begins.

Referring again to FIG. 2, as the circuit comes up to operational level,V₃ attains the level of V_(ref), i.e. 6 volts. Light is directed fromthe heating elements of the toaster onto the surface of the bread to betoasted and is reflected onto a light sensitive device such as LDR 32.During the early phase of the process, the reflected light is increasingin intensity as the heating elements approach full illuminationintensity thereby causing the resistance value of LDR 32 to decrease,(FIG. 5). In addition, the bread may be moist and will need to passthrough a "cooking" phase to dry the bread to a condition sufficient tobe receptive to a "browning" phase. In this instance, the reflectedlight also may be increasing due to the changing nature of the breadfrom moist to dry. In any event, the reflected light is increasing inintensity during the early phase.

As the resistance of LDR 32 decreases, the differential in voltage levelbetween V₁ and V₂ changes slightly resulting in a slight decrease in V₃at the output of op-amp 30. The decrease in V₃ is coupled to thenegative input of op-amp 42 resulting in the development of V₄ at theoutput of the op-amp. V₄ is then coupled through diode 44 to chargecapacitor 46. The level of charge of capacitor 46 is then representativeof the most recent maximum intensity level of the reflected light. Thus,as long as the intensity of the reflected light continues to increase,capacitor 46 will continue to charge in the context of a peak holdingcircuit.

During this period of increase of the intensity of the reflected light,the charge level of capacitor 46, i.e., V₁, appears at the positiveinput of op-amp 30. Since the charging of capacitor 46 is directlyproportional to the decrease in V₂, and as illustrated in voltage-timegraphs (a) and (b) of FIG. 4, V₁ and V₂ tend to track along the samevoltage curve. Thus, with V₁ and V₂ maintaining a generally constantdifferential as time increases, V₃ appears to remain generally constantat the level of V_(ref). However, it is recognized that slightvariations in V₂ and V₃ are occurring as the resistance of LDR 32decreases in response to increasing intensity of the reflected light tothereby effectively charge capacitor 46.

Eventually, the bread begins to brown as represented by the "browningstarts" line which extends vertically through graphs (a)-(e) of FIG. 4,and Rm in FIG. 5. As the bread begins to brown, the intensity of thereflected light begins to decrease and the resistance value of LDR 32begins to increase whereby V₂ begins to decrease as illustrated in graph(b) of FIG. 4. As V₂ decreases, V₃ increases as shown in graph (c) ofFIG. 4 and the output V₄ of op-amp 42 decreases. Normally, capacitor 46would start to discharge through op-amp 42. However, diode 44 preventscapacitor 46 from discharging whereby the capacitor "holds" the chargerepresenting the maximum light-reflected intensity detected by LDR 32.

Since the charge of capacitor 46 serves as the source of V₁, V₁ isthereafter at a constant level as illustrated in graph (a) of FIG. 4.

Thus, V₁ (.i.e., the charge on capacitor 46) becomes a standard orreference representing maximum reflected light intensity of the bread(Rm in FIG. 5) and a value against which subsequent instantaneous"browning" reflected light values (ΔR in FIG. 5) can be compared.

As the browning of the bread continues, the reflected light intensitydecreases whereby V₂ continues to decrease (graph (b) of FIG. 4) and V₃continues to increase (graph (c) of FIG. 4). As shown on graph (c) ofFIG. 4, a 50 Hz or 60 Hz ripple of up to 200 millivolts develops on V₃as a result of ambient lighting conditions. V₃, with the ripple ridingthereon, is fed to the positive input of op amp 48 where the output ofthe op amp appears as V₅ which is coupled through diode 50 to develop V₆as illustrated in graph (d) of FIG. 4. The ripple is effectively removedor reduced then by op-amp 48 and diode 50 also as illustrated in graph(d) of FIG. 4.

V₆ increases as V₃ increases and is coupled to the positive input of the"done" comparator 26. As V₆ increases to a level equal to V_(B), whichis the voltage setting of potentiometer 22, the bread has attained thedesired browness as established by the user in setting the potentiometerand the output of comparator 26 goes high as illustrated in graph (e) ofFIG. 4 to develop a "done" signal.

The "done" signal is coupled to flip-flop 58 as illustrated in FIG. 3whereby the Q output thereof resets timer 64 which begins to count atthe pace of the CLOCK signal. After a lapse of about a half-second toblock noise pulses which may be occurring during the transition of thisshut-down period, the Q6 output of timer 64 goes high which is coupledthrough an OR gate 76 to the "A" input of AND gate 66. Since "B" inputof AND gate 66 is high through the RESET signal as noted previously, theoutput of the AND gate will now go high resulting in the firing of SCR72. When SCR 72 fires, the solenoid is actuated whereby the heaterelements are turned off and the bread elevator rises to position thebrowned bread for removal from the toaster.

Thus, the electronics of the toaster provides facility for establishingan initial reference to standard (i.e., maximum light reflection of thebread to be toasted) against which successively increasing degrees ofbrowness (i.e. instantaneous light reflection of the surface of thebread as it is being browned) will be measured to obtain a browningsignal which is compared with a user-set voltage level representative ofthe desired level of browness. A match between the browning signal andthe user-set voltage level results in a shut down of the heater elementsand ejection of the browned bread. Also, by establishing the referenceor standard based on maximum light reflectivity of the particular breadto be browned, different types of bread (white, rye, wheat, etc.) can beeffectively toasted to the same degree of browness.

Referring again to FIG. 2, if only warming of the bread or a very slightlevel of browness is desired, the user will set the center arm ofpotentiometer 22 so that V_(B) is only slightly lower than V_(A), e.g.at 6.03 volts. At such a low setting, it is feasible that slight changein browness will be insufficient to develop the sensitivity in the lightreflection system including LDR 32 to the extent that comparator 26 maynot develop a "done" signal.

Therefore, to enable the desired slight browness effect for low settingsof potentiometer 22, the center arm of the potentiometer is coupled tothe negative input of comparator 24 and compared with the input to thepositive input thereof. Since the positive input of comparator 24 isalways at the level of 6.04 volts, for any input of the negative inputthereof which is below 6.04 volts, the output of the comparator will behigh and represents a "warmup" signal.

Referring to FIG. 3, when the toaster is initially operated, the "B"input of an AND gate 78 goes high. When the "warmup" signal is developedat the output of comparator 24 (FIG. 2), the "A" input of AND gate 78goes high whereby the output of the gate goes high. This high is coupledthrough an OR gate 80 and is applied to the "A" input of an AND gate 82.After 35 seconds from start up of the operation of the toaster haslapsed, the 35-second signal is developed by timer 60 and is coupled asa high to the "B" input of AND gate 82 whereby the output of the gategoes high. This high is coupled through OR gate 76 whereby the solenoidis eventually actuated in the matter previously described to terminatethe operation of the toaster and eject the bread.

In this manner, when the center arm of potentiometer 22 is set at thelow end of the voltage range (i.e., below 6.04 volts), the toaster willoperate for 35 seconds thereby providing a warming of the bread and,possibly, with a slight browning thereof.

When input "B" of AND gate 78 goes high, input "A" of an AND gate 86goes low by virtue of inverter 84 to disable the gate 86 during theperiod of normal "warmup" operation as controlled internally of thetoaster through the output of comparator 24. Thus, the output of ANDgate 86 will be low even though input "B" of the gate goes high when thetoaster is initially operated.

A warmup cycle can be initiated externally of the toaster by connectinga low to terminal 88 and a high to terminal 90. In this manner, the lowon terminal 88 is applied to input "B" of AND gate 78 to disable thegate while each of the inputs "A" and "B" of AND gate 86 go high wherebythe output of AND gate 86 goes high. This high is coupled through ORgate 80 and the procedure continues as described above to terminateoperation of the toaster after a lapse of 35 seconds.

As previously noted, timer 60 also develops a high output after a lapseof 135 seconds from initial operation of the toaster, provided thatoperation of the toaster has not been previously terminated. This highis coupled through OR gate 76 whereby the solenoid is operated asdescribed above to terminate operation of the toaster. This featureprovides a failsafe facility which insures that the operation of thetoaster will be terminated within a safe time period regardless of thefailure of the browning and warming facilities of the toaster. Also, thefailsafe facility will operate in the event the toaster had beenoperated without the insertion of bread.

A further embodiment in the form of a microprocessor circuit is shown inFIG. 7 and which functions similarly to the analogue circuit abovedescribed but, additionally, has a keypad for entering toasting valuesfor different foods, and for storing and cancelling those values.Further, an A/D convertor is used together with an EEPROM to store aprogramme for such operation. A microprogram suitable for such a furtherembodiment is listed as follows:

    __________________________________________________________________________    ;        toaster control program                                              ;        equates                                                              ;                                                                             000C                                                                             INSEMS                                                                              " OC ; COMMAND FOR 834 CHAN 0                                        000E                                                                             INPUT = OE ; COMMAND FOR 834 CHAN 1                                        0000                                                                             SELAD = OO ; SELECT A TO D CONVERTER                                       0001                                                                             DESELA                                                                              = 01 ; DESELECT A TO D CONVERTER                                     0005                                                                             SOLON = 05 ; COMMAND TO TURN SOLENOID ON                                                   AND TOASTER OFF                                               0006                                                                             TIMES1                                                                              = 06 ; COUNT FOR RESISTANCE                                                          INCREASING                                                                  ; COUNT ACTUALLY =16-TIMES1                                        TIMES2                                                                              = 0A ; COUNT FOR TOAST DONE                                                        ; COUNT ACTUALLY =16-TIMES2                                     000C                                                                             PAGE  = OC ; PAGE ADDRESS OF TABLE FOR LOID                                                INSTRUCTION                                                                 ; TABLE LOCATED AT START OF                                                     PAGE 7                                                        000F                                                                             SUBO  = OF ; MUST SUBTRACT 1 (ADD FF) TO AD                                                VALUE DURING GT TEST                                          000F                                                                             SUB1  = OF ; TO OFFSET ERRORS INTRODUCED BY                                                JITTER IN LSB OF A TO D                                       0005                                                                             BURNT = 05 ; BURNT TOAST SENSE FOR TESTING                                                 A TO D INPUT                                                                ; IF A TO D = "BO" THEN TOAST                                                   MUST BE BURNT                                                    ;                                                                             ;                                                                          000                                                                              DTO   = 00 ; LO NIBBLE FOR DELAY ROUTINE                                                   COUNTER                                                       0008                                                                             DTI   = 08 ; MID NIBB. ONES COMPLEMENT                                                     USED                                                          000F                                                                             DT2   = OF ; HI NIBBLE =100 MILLISECONDS                                      ;          ; ACTUALLY EBO = 100 MSEC BUT                                                 ; THIS TOO SLOW TO POLL KEYPAD                                                ; INPUT                                                            ;                                                                          0000                                                                             ODFO  = 00 ; LO NIBBLE FOR SOLENOID DELAY                                                  ROUTINE                                                       0000                                                                             DTFI  = 00 ; MID NIBBLE ONES COMPLEMENT                                    0101                                                                             DTF2  = 01 ; HI NIBBLE S0L. ON FOR                                                         APPROX LONG TIME                                                 ;                                                                          0000                                                                             DT10  = 00 ; LO NIBBLE FOR INITIAL DELAY                                   0000                                                                             DT11  = 00 ; MID NIBBLE 2'S COMPLEMENT                                     0001                                                                             DT12  = 01 ; HI NIBBLE MAKE IT A LONG DELAY                                   ;                                                                             ;                                                                             ;                                                                          ;        RAM USEAGE                                                           ;                                                                             000E                                                                             ADO   = 0,0E                                                                             ; A TO D LOW NIBBLE FOR SENSOR                                  000F                                                                             AD1   = 0,0F                                                                             ; A TO D HI NIBBLE FOR SENSOR                                   000C                                                                             POTO  = 0,0C                                                                             ; A TO D LO NIBBLE FOR POT                                                      SETTING                                                       000D                                                                             POT1  = 0,0D                                                                             ; A TO DE HI NIBBLE FOR POT                                                     SETTING                                                       0009                                                                             CMT   = 0,09                                                                             ; COUNTER FOR AVERAGING                                            ;                                                                          0019                                                                             STAT  = 1,09                                                                             ; STATUS INFO FOR ARITHMETIC                                                    TESTS                                                                       ; BIT 0 =1 NOT EQUAL                                            __________________________________________________________________________

The claim defining the invention are as follows.

I claim:
 1. A control arrangement for an electric food heating devicehaving heating elements for heating foodstuff and said heating elementsproviding a source of light impinging on the foodstuff, the controlarrangement comprising:a peaking circuit to determine maximum reflectedlight from the foodstuff and provide a first signal, and measuringsubsequently reflected light from the foodstuff and providing a secondsignal, said peaking circuit including an amplifier directly responsiveto the maximum reflected light for initiating the development of thefirst signal and further for determining the difference between thefirst and the second signals, and providing a third signal; and acomparator means for comparing the third signal and a preset signal, thepreset signal developed independently of the third signal and beingproportionate to a desired heating heating level, the comparator meansproviding a terminating signal to deactivate heating when the presentand the third signals are substantially equal.
 2. A control arrangementas claimed in claim 1, wherein the heating level corresponds to adesired browning level.
 3. A control arrangement as claimed in claim 1,further including:a timed circuit for warming or lightly toasting thefoodstuff, independent of the peaking circuit, comprising a first timedsignal operative to deenergize the heating elements after a preset time.4. A control arrangement as claimed in claim 1, further including:afailsafe circuit adapted to deactivate the heating elements after aprescribed time, the failsafe circuit providing a second timed signaloperative to deenergize the heating elements after the prescribed time.5. A control arrangement as claimed in claim 3, further including:afailsafe circuit adapted to deactivate the heating elements after aprescribed time, the failsafe circuit providing a second timed signaloperative to deenergize the heating elements after the prescribed time.6. A control arrangement as claimed in claim 1, further comprising aninitial delay circuit for avoiding power-on glitches.
 7. A controlarrangement as claimed in claim 3, wherein during warming or lightlytoasting foodstuff, said preset signal is provided by a fixed voltagedivider.
 8. A control arrangement as claimed in claim 1, wherein saidpreset signal is provided by a source of first voltage, said presetsignal being a fraction of said first voltage and being determined inconjunction with a first voltage divider.
 9. A control arrangement asclaimed in claim 8, wherein said preset signal is further provided by asource of second voltage, the second voltage being of larger magnitudethan the first voltage and being coupled via the first voltage divider,the present signal being of a magnitude substantially between said firstand said second voltages.
 10. A control arrangement as claimed in claim1, 8 or 9, wherein the present signal is subtracted from the thirdsignal.
 11. A control arrangement as claimed in claim 1, furthercomprising a first voltage source coupled to a second voltage divider,the divider providing a divided signal to be compared with said presetsignal and providing a warm signal when said divided and said presetsignals are substantially equal, the warm signal serving to deactivateheating when the foodstuff is slightly browned.
 12. A controlarrangement as claimed in claim 11, wherein the preset signal isprovided by a first voltage divider coupled to said first voltagesource.
 13. A control arrangement as claimed in claim 12, wherein thefirst voltage divider is also coupled to a source of second voltage, thesecond voltage being larger in magnitude than said first voltage.
 14. Acontrol arrangement as claimed in claim 1, further comprising a sourceof first voltage coupled to said peaking circuit, and wherein said firstsignal is provided in response to the differential between said firstvoltage and a heating level voltage representative of the heating ofsaid foodstuff.
 15. A control arrangement as claimed in claim 1 or 14,wherein the first signal is stored in a voltage storage means, andwherein a unidirectional current element is coupled to the storage meansto substantially prevent discharge of said first signal.
 16. A controlarrangement as claimed in claim 1, wherein the peaking circuit includesa first amplifier coupled to provide a heating signal indicative of thelevel of foodstuff heating, anda second amplifier coupled to the firstamplifier and forming a feedback loop therewith, the second amplifieradapted to provide said first signal in proportion to the differencebetween said heating signal and a reference signal.
 17. A controlarrangement as claimed in claim 1, wherein the peaking circuit includesa light receiving element adapted to determine the magnitude of saidfirst signal.
 18. A control arrangement as claimed in claim 16, whereina light receiving element is coupled to vary the gain of said firstamplifier in response to the measure of reflected light.
 19. An electricfood heating device including a control arrangement according to claim15.
 20. A control arrangement for a food heating device having heatingelements for browning foodstuff and said heating elements providing asource of light impinging on the foodstuff, the control arrangementcomprising:means for determining maximum reflected light from thefoodstuff and providing a first signal in response thereto; means formeasuring subsequently reflected light from the foodstuff and forproviding a second signal in response thereto; said means fordetermining maximum reflected light also being adapted to determine thedifference between the first and the second signals and provide a thirdsignal representative of the difference; means for establishing a presetsignal independently of the third signal which is proportionate to adesired level of browning of the foodstuff; and comparator means forcomparing the third signal and the preset signal, the comparator meansproviding a terminating signal to deactivate browning when the presetand the third signals are substantially equal.
 21. An electric foodheating device including a control arrangement according to any one ofclaims 1-9, 11 to 14 and 16 to
 20. 22. In a toaster, a peak detectorcomprising:a light detector for providing a first output proportionateto light received by said detector, a first amplifier coupled to saiddetector, the first amplifier having a gain proportionate to said firstoutput, the first amplifier also coupled to a first reference, andhaving a second output, a second amplifier coupled to said firstamplifier so as to form a closed or feedback loop, the second outputbeing provided to said second amplifier together with a second referenceand providing a third output, the third output being provided to astorage means and to said first amplifier, the storage means providingan indication of the measure of a peak level detected.
 23. A peakdetector as claimed in claim 22, further comprising:a diode meansinterposed said third output and said storage means, the diodesubstantially preventing leakage of said third output.
 24. A peakdetector as claimed in claim 22 or 23, wherein the third output isproportional to the difference between the second output and said secondreference.
 25. A peak detector as claimed in claim 22, wherein saidthird output is feedback to said first amplifier to provide a measure ofchange of said first output.
 26. A toaster including a peak detector asclaimed in any one of claims 22, 23 or
 25. 27. A toaster as claimed inclaims 26, further including a variable voltage divider coupled to saidsecond reference for providing a desired foodstuff heating level signal.28. A toaster as claimed in claim 27, further including a comparatoradapted to provide a done signal when said second output substantiallyequals said desired level signal, the done signal effecting deactivationof foodstuff heating.
 29. A toaster as claimed in claim 26, furtherincluding a control arrangement having an independent timer circuit forwarming or lightly toasting the foodstuff prior to normal toasting, saidtimer circuit being adapted to provide a timed signal operative tode-energize toasting elements of the toaster after a preset time.
 30. Atoaster as claimed in claim 26, further including a control arrangementhaving a failsafe circuit adapted to deactivate toasting elements of thetoaster after a prescribed time, the failsafe circuit providing a timedsignal operative to de-energize the toasting elements after theprescribed time.
 31. A toaster as claimed in claim 27, further includinga control arrangement having an independent timer circuit for warming orlightly toasting the foodstuff prior to normal toasting, said timercircuit being adapted to provide a timed signal operative to de-energizetoasting elements of the toaster after a preset time.
 32. A toaster asclaimed in claim 28, further including a control arrangement having anindependent timer circuit for warming or lightly toasting the foodstuffprior to normal toasting, said timer circuit being adapted to provide atimed signal operative to de-energize toasting elements of the toasterafter a preset time.
 33. A toaster as claimed in claim 27, furtherincluding a control arrangement having a fail-safe circuit adapted todeactivate toasting elements of the toaster after a prescribed time, thefail-safe circuit providing a timed signal operative to de-energize thetoasting elements after the prescribed time.
 34. A toaster as claimed inclaim 28, further including a control arrangement having a fail-safecircuit adapted to deactivate toasting elements of the toaster after aprescribed time, the fail-safe circuit providing a timed signaloperative to de-energize the toasting elements after the prescribedtime.